48 research outputs found
Utilization of zeolitic tuffs from Romania in wastewater treatment. 1. Exploratory tests.
No full textUtilization of zeolitic tuffs from Romania in wastewater treatment. 1. Exploratory tests.
No full textEffects of Soft Encapsulation on the Receive Performance of PMUTs for Implantable Devices
No full textUltrasound (US) is a promising modality for wirelessly powering implantable devices, requiring encapsulated receivers to ensure long-term stability. Traditional hermetic packaging often limits acoustic transmission, making polymer-based encapsulation a more suitable alternative. This study investigates how implant-grade polymers, thermoplastic polyurethane (TPU), parylene-C, and medical-grade silicones (MED-1000 and MED2-4213), affect the receive performance of piezoelectric micromachined ultrasonic transducers (PMUTs). Simulations and measurements between 1 and 7 MHz show that all tested materials exhibit transmission coefficients above 94% at nanometer- and micrometer-scale thicknesses, confirming their acoustic transparency. The results show that although coated PMUTs are acoustically well matched with the surrounding water medium, the added mechanical load of the coating can hinder membrane motion and reduce the energy transferred to the PMUTs. Modeling and experimental data demonstrate that stiffer coatings, such as parylene-C, lead to a reduced sensitivity when similar thicknesses are used. Likewise, residual stress in materials like MED-1000 can also degrade the performance. These effects are not evident from acoustic transmission measurements alone, underscoring the need to assess both acoustic and mechanical properties when selecting encapsulation materials. In general, softer materials offer excellent acoustic performance for PMUT encapsulation, while stiffer materials must be applied in thinner layers to avoid impairing PMUT function
Flexible Graphene-Based Passive and Active Spinal Cord Implants
No full textThe spinal cord, considered to be the most important path of the human body, when injured induces severe motor dysfunction. Therefore, patients affected by lesions on the spinal cord, are most of the time unable to walk, stand or perform motor activities that are trivial for healthy people. To provide a better quality of life for these patients, extensive research and effort have been put by both neuroscientists and engineers to provide clinical therapies for pain relief and locomotion restoration together with dedicated platforms that could deliver these therapies. Currently, for these purposes, epidural spinal cord stimulation is widely used. Apart from being used as a method to reduce pain, it has also been proven to promote locomotion recovery. Apart from clinical trials, it is of great importance to understand the mechanisms that occur while delivering specific therapies. To this end, more exploratory research is mostly conducted in rodents. However, the availability of tailored neurotechnologies, for experiments conducted in small animals, is limited mostly due to size constraints. Moreover, when developing implantable devices that would target the spinal cord, careful selection of the materials used is equally important. However, understanding the underlying mechanism leading to a specific behaviour or motor outputs requires exploring and quantifying new methods of stimulation. For instance, optogenetics has been gaining a lot of popularity in the field of neural stimulation as it is a more specific technique that could help neuroscientists map the neuronal circuitry within the human body. Thus, apart from developing spinal cord implants that resemble best the anatomy of the body, while inducing as little stress as possible on the spinal cord, for exploratory reasons the developed implants must provide optogenetic compatibility. Therefore, this thesis reports the development as well as the characterization of both passive and active spinal cord implants with optogenetic compatibility.To achieve the desired goal of having a fully implantable, flexible spinal cord implant with optogenetic compatibility, a scalable and reproducible microfabrication process has been developed. Materials such as graphene, for transparency, flexibility and conductivity were used to develop the microelectrode arrays. Moreover, soft, polymeric encapsulation was employed to sustain the high flexibility and transparency of the implant. The end result of the microfabrication process would lead to a device consisting of a multi-layered graphene structure between two polymeric-based encapsulation layers and metal test pads for interconnection to the outside world. However, towards achieving this final structure, several challenges were encountered. Suspension of the implants after developing them on a rigid substrate, yet ensuring high quality for the graphene layer leads to several iterations of the fabrication process. Despite the challenges encountered, several prototypes were successfully developed. However, having prototypes that can only validate the process flow would not suffice. Therefore, extensive evaluation of the devices has been conducted and reported. Methods such as Raman spectroscopy and optical transmittance to evaluate the graphene layer or cyclic voltammetry and electrochemical impedance spectroscopy to characterize the performance of the fabricated devices were employed. The degree of transparency obtained using the reported microfabrication process was ~78 %, leading to the conclusion that the number of graphene layers for the final device was 10. It has been proven that graphene does not deteriorate over time when soaked in saline solution for several consecutive days and apart from that, the graphene-based implants showed no performance deterioration when bent over rods down to 3 mm in diameter. Moreover, the graphene electrodes provided impedance values of ~8 kΩ at 1 kHz frequencies, values comparable to what literature has previously reported. Apart from developing a passive graphene-based spinal cord implant, the focus of this thesis was also to fabricate and characterize an active implant. However, embedding active components with a flexible, graphene-based array of electrodes is not trivial. Therefore, system integration of small test chips was investigated and after several iterations of flip-chip bonding processes, a complete, active, graphene-based prototype was obtained. The measurements performed after the bonding process have proven that both bonding on graphene-only as well as on graphene and metal substrates is possible and the four-point measurement results indicated resistance values ranging from 10 mΩ up to 16 Ω for individual connections, depending on the substrate used.Therefore, with this research project, not only the first fully transparent, graphene-based spinal cord implants have been developed but also the results obtained from their characterization illustrate that the process is stable and the performance of the devices is promising.Biomedical Engineering | Bioelectronic
Towards a Microfabricated Flexible Graphene-Based Active Implant for Tissue Monitoring During Optogenetic Spinal Cord Stimulation
No full textOur aim is to develop a smart neural interface with transparent electrodes to allow for electrical monitoring of the site of interest during optogenetic stimulation of the spinal cord. In this work, we present the microfabrication process for the wafer-level development of such a compact, active, transparent and flexible implant. The transparent, passive array of electrodes and tracks have been developed using graphene, on top of which chips have been bonded using flip-chip bonding techniques. To provide high flexibility, soft encapsulation, using polydimethylsiloxane (PDMS) has been used. Preliminary measurements after the bonding process have shown resistance values in the range of kΩ for the combined tracks and ball-bonds.Electronic Components, Technology and MaterialsBio-Electronic
Towards a Microfabricated Flexible Graphene-Based Active Implant for Tissue Monitoring During Optogenetic Spinal Cord Stimulation
No full textThis work aims to develop a smart neural interface with transparent electrodes to allow for electrical monitoring of the site of interest during optogenetic stimulation of the spinal cord. In this paper, a microfabrication process for the wafer-level development of such a compact, active, transparent and flexible implant is presented. Graphene has been employed to form the transparent array of electrodes and tracks, on top of which chips have been bonded using flip-chip bonding techniques. To provide high flexibility, soft encapsulation, using polydimethylsiloxane (PDMS) has been used. Making use of the "Flex-to-Rigid" (F2R) technique, cm-size graphene-on-PDMS structures have been suspended and characterized using Raman spectroscopy to qualitatively evaluate the graphene layer, together with 2-point measurements to ensure the conductivity of the structure. In parallel, flip-chip bonding processes of chips on graphene structures were employed and the 2-point electrical measurement results have shown resistance values in the range of kΩ for the combined tracks and ball-bonds.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Bio-ElectronicsElectronic Components, Technology and Material
Flexible, graphene-based active implant for spinal cord stimulation In rodents
No full textThe most important symptoms of spinal cord injuries (SCIs) are partial or complete loss of sensory and/or motor functions caused by the disruption of the neural pathway between the brain and the extremities of the body. Recent studies have shown that epidural spinal cord stimulation (ESCS) can promote locomotor recovery in patients affected by SCIs, thus becoming one of the most promising means of treatment for the lesion. Devices currently available on the market, consist of active components, enclosed in a hard case and connected via leads to the electrodes that form the interface between the stimulator and the biological tissue. The presence of leads along the spine, may be an important cause of failure for the device. Moreover, the overall stiffness of the stimulator does not resemble best the anatomical structure of the human body. Flexibility and optical monitoring of the biological tissue during implantation and stimulation are very important aspects and both can be improved with a proper choice of materials. The goal of this work is to develop a compact, active, transparent and flexible spinal cord stimulator that could be implanted at the site of stimulation. To provide high flexibility, soft encapsulation, using polydimethylsiloxane (PDMS) has been used. To ensure transparency but also mechanical stability of the electrodes and tracks, graphene has been chosen as a replacement for the conventional metals. Integrating active components, in the form of application specific integrated circuits (ASICs), on a graphenebased substrate, constitutes the biggest challenge. To this end, flip chip bonding techniques using a metal layer as an interface between graphene and the chip’s stud-bumped pads, are being investigated. Preliminary measurements after bonding have shown resistance values in the range of kΩ, thus taking the project one step closer to achieving the desired goal.Electronic Components, Technology and MaterialsBio-Electronic
Soft, flexible and transparent graphene-based active spinal cord implants for optogenetic studies
No full textPatients affected by spinal cord injuries (SCI) are usually unable to perform trivial motor activities and thus, for therapeutic purposes, epidural spinal cord stimulation (ESCS) is currently used. Moreover, more exploratory research, using optogenetics, is being conducted in rodents for a better understanding of the mechanisms that occur while delivering specific therapies. However, the availability of tailored neurotechnologies for such experiments is limited. This work reports the development and characterization of flexible, active spinal cord implants with optogenetic compatibility1,2 (Fig.1). A scalable and reproducible microfabrication process has been developed, using graphene3, a transparent, flexible and conductive material, to form the electrodes and interconnects of the implant. Small and thin4 electronic chips were assembled via flip-chip bonding processes either on graphene or on metal-on-graphene layers. Soft, polymeric encapsulation was employed to sustain the high flexibility and transparency of the implant. The result is an active prototype consisting of a multi-layered graphene structure between two polymeric-based encapsulation layers, with thin chips integrated on the implant and test pads for interconnection to the outside world. Raman spectroscopy and optical transmittance were employed for the characterization of the graphene layer while cyclic voltammetry and electrochemical impedance spectroscopy were performed to benchmark the electrical properties of the device. The assembly process of the chips was evaluated using four-point electrical measurements. In this work, the first transparent, graphene-based active implants have been developed (Fig. 2 and Fig. 3). The prototypes were extensively characterized and the results showed a transparency of ~80 % as well as no deterioration over time when soaked in saline solution or when bent under various angles. The graphene electrodes showed an impedance of ~8 kΩ at 1 kHz frequencies and the resistance after the bonding process ranged from 10 mΩ up to 16 Ω for individual connections, depending on the substrate usedBio-ElectronicsElectronic Components, Technology and Material
